Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
  • G03B13/00—Viewfinders; Focusing aids for cameras; Means for focusing for cameras; Autofocus systems for cameras
  • G03B13/32—Means for focusing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N5/00—Details of television systems
  • H04N5/30—Transforming light or analogous information into electric information
  • H04N5/33—Transforming infrared radiation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
  • H04N23/20—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from infrared radiation only
  • H04N23/23—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from infrared radiation only from thermal infrared radiation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
  • H04N23/60—Control of cameras or camera modules
  • H04N23/67—Focus control based on electronic image sensor signals
  • H04N23/673—Focus control based on electronic image sensor signals based on contrast or high frequency components of image signals, e.g. hill climbing method

Definitions

• the present invention relates to the field of image processing and methodologies to passively focus an image automatically, using the electronic sensor signal.
• an object of interest can be seen in focus and with negligible blur by changing the distance between lens and optical sensor accordingly.
• methods and systems to auto-focus an image are used for example in infrared imaging systems (thermal cameras) in which there is a sensor acquiring an infrared image of the scene under consideration and generally these images are converted into a greyscale format.
• This image consists of a two dimensional array of pixels which represent the infrared intensity at these locations. Because of depth and range requirements of these systems, the depth of field is low and it is required to focus the image repetitively which lowers targeting and surveillance performance if done manually.
• passive focusing is a widely used method, wherein the signal from the electronic image sensor is evaluated and used to drive the lens motion devices which are for example; stepper motors.
• One of the problems related to the passive methods is that, they require a mathematical function which represents the sharpness of the image. A good function should be monotonically increasing with a maximum at the focus point.
• a modified Laplace operator or a Tenengrad function is used, which both determine the high frequency component of an image by evaluating directional derivatives at each pixel location.
• Another method uses local pixel variance of images which was observed to increase when the image is out-of- focus.
• Other than these Fourier transform method, total module difference method and histogram entropy method are other known methods to passively detect focus condition.
• Another problem related to the automatic focusing systems is the processing power requirements due to the high frame rate and resolution of the infrared vision systems which makes image processing difficult on generic central processing units (CPU) or digital signal processors (DSP). Instead, field programmable gate arrays (FPGA) are used to process the data by parallel processing in much less clock cycles.
• FPGA field programmable gate arrays
• Currently, many infrared vision systems are equipped both with FPGAs and DSPs which run histogram matching and edge enhancement algorithms on real-time. Current methods are not offering a simple way of focusing an infrared imaging system automatically although they can be used to auto-focus the lens with ease and very little modification using the method proposed.
• Japan patent document JP 3297282 an application in the state of the art, discloses a method for focusing an imaging system automatically by comparing derivatives of two evaluation value received from one low and one high pass filter and accordingly using one of these signals to determine lens position.
• the International patent document WO 2010088079 discloses a method for focusing an imaging system automatically using more than one digital band-pass filter which are switched according to local approximations of first and second derivative values.
• An objective of the present invention is to provide an easy to implement methodology to focus an infrared imaging system.
• Figure 1 is the schematic view of the preferred embodiment system.
• Figure 2 shows graphs of three one dimensional modified sharpness step functions.
• Figure 3 shows graphs of high frequency components of the one dimensional modified sharpness step functions.
• Figure 4 shows histograms of the high frequency components of the modified step functions.
• A, B and C stand for the first, second and third functions respectively
• Figure 5 is the flowchart of the preferred method of the present invention.
• a method for focusing an electronic imaging system (100) fundamentally comprises the following steps,
• an image of the scene under consideration is received (101).
• this will be a two dimensional grey scale pixel image, each pixel representing the infrared density for that location in the scene under consideration.
• the main aim of this system is to detect the focusing direction and a means to detect sharpness should be introduced.
• histogram width is changing as the sharpness of the function changes.
• histograms represent the distribution of pixels on the image with different values (values on horizontal axis and count on vertical) and histogram width means the scatter of the distribution around the mean value.
• pixel values at higher frequency components will get clustered around a single value on the histogram.
• Histograms are acquired for at least two different frequency components for a region on the received is calculated in step (102). Then, their widths are calculated by eliminating some of the values on the floor caused by the possible noise in the system and they are stored for further comparison (103). This introduces a noise threshold in a preferred configuration.
• the width can be found using different methods, for example by finding the intersection of the histogram graph edges with a horizontal line drawn at the noise threshold level and finding the distance in between. Since most of the infrared imaging systems already have means for edge enhancement, contrast adjustment etc, high frequency and low frequency histograms are already being generated continuously and these are used in this method. In a preferred configuration, the lower frequency components of the image are found by subtracting the higher frequency component from the original image.
• the focus lens is moved to detect the change in the histogram widths.
• the highest frequency component's histogram is used since it is assumed that there was some object in focus previously.
• Last received frame's highest frequency component histogram width and at least one previously received frame's histogram width corresponding to the same frequency component are differentiated to determine focus direction in step (104).
• the histograms with a lower frequency component are differentiated and used as the focus measure. This case occurs when the current position of the focus lens coincides to a point where image is completely out of focus and high frequency histogram is gathered tightly around its mean.
• a histogram with a wider distribution should be used instead, which is actually the case for a lower frequency component histogram.
• a meaningful direction is found using the change of the histogram width values.
• a stop signal is generated and method should be reactivated with an input means for the new state of the lens in a preferred configuration.
• This meaningful difference is a value other than zero in a preferred configuration since this would mean the derivative of the stored histogram width sequence with changing lens position is zero and no direction can be deduced.
• a focus direction is determined and a signal is generated. The focus direction signal is generated to drive the focus assembly in the direction that increases the histogram width.
• a system for focusing an electronic imaging system (1) fundamentally comprises;
• At least one image sensor (2) to acquire at least one electronic pixel image of the scene under consideration when necessary
• At least one image processing unit (3) configured to receive at least one image and implement the method for focusing an electronic imaging system (100) using this image and output a focus direction signal found by the method (100),
• image sensor (2) is a scanning infrared vision camera which is able to differentiate temperature differences in the scene.
• image processing unit (3) is configured to receive at least one image from image sensor (2).
• Image processing unit (3) is configured to transmit a signal to a lens drive mechanism (D) which locates the lens (L) according to the signal produced by the image processing unit (3).

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Automatic Focus Adjustment (AREA)
• Studio Devices (AREA)
• Focusing (AREA)

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• 2012
  • 2012-02-02 KR KR1020147005191A patent/KR101733103B1/ko active IP Right Grant
  • 2012-02-02 US US14/239,544 patent/US9596418B2/en active Active
  • 2012-02-02 WO PCT/IB2012/050487 patent/WO2013114160A1/en active Application Filing
  • 2012-02-02 JP JP2014526565A patent/JP5883141B2/ja active Active
  • 2012-02-02 EP EP12706323.8A patent/EP2735138B1/en active Active

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